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Tapuwa Mashangwa Agriculture column
IN the face of continuous climatic change and irregular global weather patterns characterised by drought and flooding, soil and water utilisation and management are paramount.

Countries with poor rainfall, non-arable land or small arable lands are producing vast quantities of agricultural produce despite being in a status that should render them agriculturally irrelevant. They are achieving this through hydroponic farming.

Hydroponics is a subset of hydroculture and is a method of growing plants using mineral nutrient solutions, in water, without soil.

Terrestrial plants may be grown with their roots in the mineral nutrient solution only or in an inert medium, such as perlite or gravel.

The earliest published work on growing terrestrial plants without soil was the 1627 and by 1929, William Frederick Gericke of the University of California at Berkeley began publicly promoting that solution culture be used for agricultural crop production. Gericke created a sensation by growing tomato vines 25 feet high in his back yard in mineral nutrient solutions rather than soil.

Today hydroponic farming is an industry on a level of its own continually developing through the application of the latest technologies that utilise and manage soil and water efficiently and effectively.

The two main types of hydroponics are solution culture and medium culture. Solution culture does not use a solid medium for the roots, just the nutrient solution. The three main types of solution cultures are static solution culture, continuous-flow solution culture and aeroponics.

The medium culture method has a solid medium for the roots and is named for the type of medium, for example, sand culture, gravel culture, or rockwool culture.

There are two main variations for each medium, sub-irrigation and top irrigation. For all techniques, most hydroponic reservoirs are now built of plastic, but other materials have been used including concrete, glass, metal, vegetable solids, and wood.

The containers should exclude light to prevent algae growth in the nutrient solution.

In static solution culture, plants are grown in containers of nutrient solution, such as glass Mason jars in-home applications, plastic buckets, tubs, or tanks. The solution is usually gently aerated but may be un-aerated.

If un-aerated, the solution level is kept low enough that enough roots are above the solution so they get adequate oxygen.

A hole is cut in the lid of the reservoir for each plant. There can be one to many plants per reservoir. Reservoir size can be increased as plant size increases. A home-made system can be constructed from plastic food containers or glass canning jars with aeration provided by an aquarium pump, aquarium airline tubing and aquarium valves.

Clear containers are covered with aluminium foil, butcher paper, black plastic, or other material to exclude light, thus helping to eliminate the formation of algae. The nutrient solution is changed either on a schedule, such as once per week, or when the concentration drops below a certain level as determined with an electrical conductivity meter. Whenever the solution is depleted below a certain level, either water or fresh nutrient solution is added. A Mariotte’s bottle or a float valve, can be used to automatically maintain the solution level.

In raft solution culture, plants are placed in a sheet of buoyant plastic that is floated on the surface of the nutrient solution. That way, the solution level never drops below the roots.

In continuous-flow solution culture, the nutrient solution constantly flows past the roots. It is much easier to automate than the static solution culture because sampling and adjustments to the temperature and nutrient concentrations can be made in a large storage tank that has potential to serve thousands of plants.

A popular variation is the Nutrient Film Technique (NFT) whereby a very shallow stream of water containing all the dissolved nutrients required for plant growth is recirculated past the bare roots of plants in a watertight thick root mat, which develops in the bottom of the channel and has an upper surface that, although moist, is in the air. Subsequent to this, an abundant supply of oxygen is provided to the roots of the plants.

A properly designed NFT system is based on using the right channel slope, the right flow rate, and the right channel length.

The main advantage of the NFT system over other forms of hydroponics is that the plant roots are exposed to adequate supplies of water, oxygen, and nutrients.

In all other forms of production, there is a conflict between the supply of these requirements, since excessive or deficient amounts of one results in an imbalance of one or both of the others.

NFT, because of its design, provides a system where all three requirements for healthy plant growth can be met at the same time, provided that the simple concept of NFT is always remembered and practised. The result of these advantages is that higher yields of high-quality produce are obtained over an extended period of cropping.

A downside of NFT is that it has very little buffering against interruptions in the flow, for example, power outages. But, overall, it is probably one of the more productive techniques.

Tapuwa Justice Mashangwa is a young entrepreneur based in Bulawayo, Founder and CEO of Emerald Agribusiness Consultancy. He can be contacted on +263 739096418 and email: [email protected]